a) Field of the Invention
The invention is directed to a vacuum valve comprising a valve housing with a valve opening having a longitudinal axis and a valve seat, a valve plate which is displaceable in a straight line in a displacement direction between an open position in which it releases the valve opening and a closed position in which its contacts the valve seat of the valve housing and closes and seals the valve opening, this valve plate being arranged on at least one valve rod which is displaceable axial to the displacement of the valve plate, a flexible sealing ring which is arranged at a front side of the valve plate or at the valve seat of the valve housing, a sealing surface which is arranged at the valve seat of the valve housing or at the front side of the valve plate and which is contacted by the sealing ring in the closed position of the valve plate, wherein the sealing surface and the sealing ring are arranged in parallel planes which are inclined relative to the displacement direction around an axis extending at right angles to the displacement direction of the valve plate and at right angles to the longitudinal axis of the valve opening.
b) Description of the Related Art
Valves in which the sealing surface and the sealing ring lie in parallel planes that are inclined relative to the displacement direction of the valve plate around an axis extending at right angles to the longitudinal axis of the valve opening are known as wedge gate valves. Valves of this type are not normally used for vacuum applications but as fluid valves. A fluid valve of this kind is disclosed, for example, in U.S. Pat. No. 2,194,261. Other wedge gate valves are known, for example, from U.S. Pat. Nos. 4,548,386 and 5,013,009.
In vacuum valves with valve slides having elastomer seals, however, it is usually required when the valve plate is moved into its closed position to ensure that the seal is not loaded transverse to its longitudinal direction from the moment it contacts the sealing surface. A shear stress of this kind acting on the seal is generally considered very disadvantageous with respect to the life of the seal.
Therefore, in vacuum technology valve slide constructions are usually designed in such a way that the closing movement of the closure member is carried out at least substantially perpendicular to the sealing surface of the valve seat in the final segment of the closing movement.
In a first conventional embodiment form of a gate valve of the type mentioned above, the valve plate is initially displaced in a displacement direction by an actuating device for closing the valve until it is in a position that is located opposite from the valve opening but is raised from the valve seat. Subsequently, a movement is carried out perpendicular to the sealing surface, i.e., in direction of the longitudinal axis of the valve opening, so that the valve plate is moved toward the valve seat. The second step of the closing movement in gate valves of this kind is achieved in different ways, for example, by lever mechanisms, rolling bodies which are guided in wedge-shaped gaps between the valve plate and supporting plate, by tilting elements, and so on. In order to avoid bending the valve rod in the second step of the closing movement, a counter-plate is provided which is moved simultaneously toward a wall of the valve housing across from the valve seat. In another type of plate valve or slide valve, the second step of the closing movement is carried out in that the valve rod is swiveled around a fulcrum.
A gate valve or slide valve of the type mentioned above in which, in order to close the valve, the valve plate is initially displaced into a position that is located opposite from the valve seat but is raised from the valve seat and subsequently contacts the valve seat substantially perpendicular to the sealing surface is known, for example, from U.S. Pat. No. 6,629,682 B2. In order to protect the sealing ring from corrosive process gas acting on the material of the sealing ring in the closed state of the valve and to reduce the stress on the sealing ring in the closed state of the valve so that the sealing ring is less susceptible to the corrosive process gases, a supporting ring made of plastic is provided in this valve in addition to the sealing ring. This supporting ring lies closer to the valve opening than the sealing ring when viewed from the latter and limits the pressing force acting on the sealing ring in the closed state of the vacuum valve. Apart from a one-piece construction of the sealing ring and supporting ring, constructional variants in which a separate sealing ring and supporting ring are provided are also described.
U.S. Pat. No. 3,722,852 also discloses a sealing ring that is arranged perpendicularly against a seal and is supported by a supporting ring surrounding the sealing ring. It is also known to provide a circumferentially extending raised portion or projection at the valve plate, which projection is integral with the valve plate and contacts a surface surrounding the valve opening in the closed state of the valve so that the deformation of the sealing ring is limited.
In another type of plate valve or slide valve, the sealing surfaces and the surface at which the elastomer seal is arranged are constructed in a three-dimensional manner such that no shear stresses act on the elastomer seal when the valve plate moves into the valve seat in a straight line. The valve plate is displaced in a straight line along its entire displacement path between the open position and closed position. The forces act on the seal either substantially only in the direction perpendicular to the sealing surface or with an additional force component oriented in longitudinal direction of the seal. Accordingly, no shear forces act on the sealing ring. A vacuum valve of this kind is known, for example, from U.S. Pat. No. 4,921,213. In this valve, the sealing surface and the sealing ring do not lie in a plane and a portion of the sealing ring is arranged at a front end portion of the valve plate considered in the inward movement direction of the valve plate. This slide valve is disadvantageous in that sealing rings with relatively complicated shapes must be used; these sealing rings cannot be formed as O-rings inserted into a groove for larger nominal widths but must be vulcanized to the valve plate. Therefore, the entire valve plate must be exchanged when the sealing ring is damaged.
A vacuum valve of the type mentioned in the beginning is known from U.S. Pat. No. 6,367,770 B1. The valve plate has front and back sides that taper toward one another in the shape of a wedge, a circumferentially closed sealing ring being arranged respectively at these front and back sides. In order to prevent shear loads on the sealing rings to a great extent, the closing force that can be applied to the valve plate by the actuating member is only very small. When closing, the valve plate accordingly contacts the valve seat only slightly without substantial pressing of the sealing ring. Pressing of the sealing ring and a complete sealing of the valve are achieved only when a differential pressure is present between the sides of the valve and presses one of the two sealing rings against the sealing surface. However, a complete closing (i.e., sealing) of the valve is not possible without a differential force of this kind.